Characterizing the Gender Differences of Multidrug-resistance Peptide (MRP) Transporter Expression in Mouse Blood-brain Interfaces

The choroid plexus (CP) and blood-brain barrier (BBB) control the movement of several drugs and endogenous compounds between the brain and systemic circulation. The multidrug resistance associated protein (Mrp) efflux transporters form part of these barriers. Several Mrp transporters are positively regulated by the transcription factor nuclear factor erythroid-2-related factor (Nrf2) in liver. The Mrps, Nrf2 and Nrf2-dependent genes are cytoprotective and our aim was to examine basal gender differences in expression of Mrp transporters, Nrf2 and Nrf2-dependent genes (Nqo1 and Ho-1) in the brain-barriers. Previous studies have shown higher expression of Mrp1, Mrp2 and Mrp4 in female mouse liver and kidney. We hypothesized that similar renal/hepatic gender-specific patterns are present in the brain-barrier epithelia interfaces. qPCR and immunoblot analyses showed that Mrp4, Ho-1 and Nqo1 expression was higher in female CP. Mrp1, Mrp2 and Nrf2 expression in the CP had no gender pattern. Female Mrp1, Mrp2 and Mrp4 mouse brain expressions in remaining brain areas, excluding CP, were higher than male. Functional analysis of Mrp4 in CP revealed active accumulation of the Mrp4 model substrate fluo-cAMP. WT female CP had 10-fold higher accumulation in the vascular spaces than males and 60% higher than Mrp4-/- females. Probenecid blocked all transport. Methotrexate did as well except in Mrp4-/- females where it had no effect, suggesting compensatory induction of transport occurred in Mrp4-/-. Collectively, our findings indicate significant gender differences in expression of Mrp transporters and cytoprotective genes in the CP and BBB. In addition to identifying the basal gender differences of these transporters, another goal of the present study was to examine the gender differences of these genes in lateral CP and brain (with the lateral CP removed) in the response to an hepatotoxic dose of acetaminophen (APAP) in wild-type (WT) and Nrf2-/- mice. We also ascertained the gender-dependent response to APAP of Cyp2e1, an enzyme responsible for the bioactivation of APAP to reactive intermediates and expressed equivalently in WT males and females. Our results indicate that hepatotoxic doses of APAP increase Abc drug transporters gene expression in male, but not female mouse CP and brain. There are no gender-dependent differences or induction after APAP in Cyp2e1 expression in CP or brain. Together, the data suggest that gender dependent expression of stress response genes (Nqo1 and Ho-1) and Mrps at blood-brain interfaces may influence the potential neurotoxicity of APAP differentially in males and females